The most necessary condition for a high quality welded joint is a well-formed weld without faults such as incomplete fusion, collars, and undercuts.
In conventional methods of arc welding with the speed of feeding the consumable electrode substantially (e.g. by a factor of 2 to 200) higher than the welding speed, these faults appear at a welding speed above 70 meters per hour (m.p.h.). At such a speed, the base metal has not enough time to get thoroughly warmed before the welding arc is applied, and incomplete fusion and undercuts are liable to occur. Besides, such methods fail to provide a uniformity of width and reinforcement of weld.
Nevertheless, modern production practice requires a speed of welding significantly higher than 70 m.p.h. (up to 150 m.p.h. or more). To eliminate said faults, multi-arc welding is employed and this involves the use of complicated equipment, bulky and inconvenient in operation.
There is known in the art a method of single-arc welding where the workpiece is fixed with a certain slope to the direction of welding so as to cause the liquid metal of the molten pool to flow in the welding direction under the effect of gravity, while the electrode is fixed with a backward slope of 10 to 15 deg. in relation to the direction of welding. This method of welding provides a better warming-up of the base metal before the welding arc is applied, thus making it possible to get a weld having satisfactory strength properties with high welding speeds (up to 300 m.p.h.).
The main shortcoming of the above method is its impracticability for workpieces which cannot be fixed with a required slope because of their construction, overall dimensions or production conditions which narrows the field of application of this method. Besides, although the weld obtained by said method exhibits satisfactory strength properties, it still has undercuts, incomplete fusion, collars, and lacks uniformity of width and reinforcement.
Known in the art is a method of single-arc welding with automatic feed of the consumable electrode of a round cross-section, wherein the above drawbacks are overcome (FRG Patent No. 1814325). According to this method, welding is carried out by an electrode with its end submerged in a molten pool using a wire electrode, flux and a heavy current (1000 to 4000A). In accordance with this method, the diameter of the wire electrode is chosen according to the welding current: with the current of 1500 to 2500A, it equals 6 to 8 mm, with the current above 2500A, it is at least 7 mm.
This method aims to obtain a high quality weld for high-speed arc welding (up to 300 m.p.h.).
The shortcoming of this method is that its application is limited to submerged arc welding at heavy currents. Moreover, the limited lowest diameter of the electrode makes it impossible to obtain sufficiently small welds, the minimum weld width being limited to no less than 7 mm.